Two most common plant pathogen disseminated through contaminated irrigation waters are Pythium and Phytophthora.  Pythium is mainly a problem during propagation and growth of herbaceous material.  Phytophthora is an important pathogen on a number of ornamental crops. It can cause root rot, cankers, and foliar blights. Cankers and foliar blights are readily diagnosed since the symptoms are apparent. Root rots are more difficult to diagnosed since the roots are obscured from view. Early symptoms of stunting may not be readily apparent in a block of plants that are uniformly infested. Severe symptoms include mimics of nutrient deficiency damage symptoms, and eventual plant death. Phytophthora is easily spread through water and can be present in irrigation water when irrigation runoff is recycled. Ponds, irrigation water, and soil can be tested for the presence of Phytophthora. Tests for the presence of Pythium are misleading since there are a number of species that are found in irrigation water but do not cause important diseases. Anyone who irrigates with surface water is potentially at risk of contamination from Phytophthora. Facilities that catch runoff and reuse it for irrigation are especially at risk. A large number of ornamental plants are particularly susceptible to diseases caused by various species of Phytophthora. Producers of these crops should consider testing for Phytophthora. If diseased plants have been diagnosed with Phytophthora, testing may help determine the source and distribution of Phytophthora. Producers that use well water or municipal water sources do not need to have water tested. Pond sampling is the most sensitive method but requires access to the pump intake in the pond. Irrigation water sampling is not as sensitive but more convenient. Soil are tested using a baiting technique to recover the Phytophthora.